Setting up a culture of cells is a relatively simple task. All you need is some media, which would be a solution that contains all the ingredients needed for cell growth, and some cells, obtained from another previous culture. Put simply, you fill a container with media and add a small amount of cells. These cells then do what cells do – they divide and form a large population of cells over time. In other words, the machinery within the cells converts the simple biomolecules in the media into new cells.

But now I have a puzzle for you.

Lets begin by making a media with the following ingredients: amino acids, glucose, vitamins, nucleosides, salts and citrate. Next, let’s transfer a single Tetrahymena cell to 1 microliter of the media. That corresponds to a density of 1000 cells per ml. What happens? The cell does what cells do – it divides and forms a population of cells.

But what happens if you transfer a single Tetrahymena cell to 10 microliters of media (which corresponds of 100 cells per mi.)? Answer – it dies.

So why does this single-celled organism die when it is surrounded by an abundance of food and there are no predators or toxins around?

I’ll give ya the answer.